Dear Rick,
suddenly the application I use to send emails in the background from my development computer no longer sends emails.
Apparently nothing has changed, the parameters are always the same, yet the emails don't go out.
The application uses the classic method

m.oSmtp = CREATEOBJECT ("wwSmtp")

The email provider confirmed to me that the parameters are correct.
I also tried to completely uninstall BitDefender Internet Security but the problem did not go away.
I tried to send emails also with parameters of other accounts, but without success.
Fortunately I am able to send emails from Outlook.
What may have happened?
Some files may be corrupted?
Or is it Windows 10 that has decided to block the sending of emails?
Thank you very much for support

No way to know. What is the error message?

There are lots of reasons this can happen. Search here - I posted a message just a week ago with a lot of reasons why email can be rejected...

+++ Rick ---

Unfortunately the return error message is quite generic: "error while sending mail".
I will try to investigate.
Thank you very much again.